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            <div class="quiz-header">
              <h1>原子操作类Atomic - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
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  {
    "question": "根据文档，在多线程环境下对共享计数器（如 `count`）执行自增操作时，如果不使用原子操作或锁，最可能导致什么问题？",
    "options": [
      "程序会因 `ConcurrentModificationException` 异常而崩溃。",
      "最终的计数值将大于预期值，因为线程会重复执行自增操作。",
      "系统性能会急剧下降，但计数值最终是正确的。",
      "最终的计数值将小于预期值，因为多个线程可能读取到相同的旧值并覆盖彼此的写操作。"
    ],
    "correctAnswerIndex": 3,
    "explanation": "文档中的例子清楚地说明了，如果两个线程同时读取旧值（例如5），各自加1得到6，然后分别写回，最终结果是6而不是期望的7。这种情况被称为“竞态条件”，它会导致更新丢失，使得最终结果小于预期。",
    "source": "文档中「原子操作的意义」部分",
    "hint": "回想一下文档中举的两个线程同时对计数器 `count` 进行自增的例子，最终结果是什么？"
  },
  {
    "question": "Atomic 类能够实现高效的无锁（lock-free）原子操作，其底层的核心技术是什么？",
    "options": [
      "CAS (Compare and Swap) 机制，这是一种乐观锁技术。",
      "`synchronized` 关键字，这是一种悲观锁机制。",
      "`volatile` 关键字，它仅保证内存可见性。",
      "线程的 `join()` 方法，用于等待线程结束。"
    ],
    "correctAnswerIndex": 0,
    "explanation": "文档在多个章节中明确指出，Atomic类的原子性操作是基于 CAS (Compare and Swap) 机制实现的。CAS是一种乐观锁技术，它通过比较内存中的当前值与期望值是否相等来决定是否执行更新，从而避免了传统锁机制带来的线程阻塞和性能开销。",
    "source": "文档中「Atomic介绍」部分",
    "hint": "这是一种乐观锁技术，它通过“比较”和“交换”两个步骤来完成原子更新。"
  },
  {
    "question": "除了保证操作的原子性，Atomic类还提供了哪个至关重要的特性来确保一个线程对共享变量的修改能被其他线程立即看到？",
    "options": [
      "自动的死锁检测与恢复。",
      "内存可见性（Memory Visibility）。",
      "事务隔离级别控制。",
      "线程优先级自动调整。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "文档明确指出，Atomic类通过内部的内存屏障和volatile变量来实现内存可见性。这意味着当一个线程使用Atomic类的方法修改了共享变量后，这个修改会立即对其他所有线程可见，从而防止了因数据缓存导致的不一致问题。",
    "source": "文档中「Atomic 类的特性与优势」部分",
    "hint": "这个特性确保了线程之间不会看到“过时”的数据。"
  },
  {
    "question": "在并发编程中，一个共享变量的值可能从A变为B，然后又变回A。如果一个线程只检查当前值是否为A就进行更新，可能会出现问题。哪个Atomic子类是专门为了解决这种“ABA问题”而设计的？",
    "options": [
      "AtomicReference",
      "AtomicBoolean",
      "AtomicStampedReference",
      "AtomicInteger"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档在“注意事项”部分提到了ABA问题，并指出可以使用 `AtomicStampedReference` 来解决。该类在更新引用时，不仅会比较引用的值，还会比较一个“版本号”（stamp）。只有当值和版本号都符合预期时，更新才会成功，从而有效避免了ABA问题。",
    "source": "文档中「Atomic注意事项」部分",
    "hint": "解决这个问题需要一个不仅关心“值”，还关心“版本”的原子类。"
  },
  {
    "question": "如果你需要为一个系统的在线用户数设计一个线程安全的计数器，并且希望在高并发下获得比使用`synchronized`更好的性能，以下哪个类是最佳选择？",
    "options": [
      "AtomicInteger",
      "AtomicReference<Integer>",
      "普通的 `int` 配合 `ReentrantLock`",
      "AtomicBoolean"
    ],
    "correctAnswerIndex": 0,
    "explanation": "根据文档描述，`AtomicInteger` 专用于原子更新整型数据，非常适合用作计数器、ID生成器等场景。它基于无锁的CAS机制，相比于需要加锁的`synchronized`或`ReentrantLock`，在高并发场景下通常具有更高的性能和吞吐量。",
    "source": "文档中「Atomic的常用子类」部分",
    "hint": "文档中有一个专门用于原子更新整型数据的类，非常适合计数器场景。"
  },
  {
    "question": "文档在“注意事项”中提到，Atomic类并不能解决所有的线程安全问题，特别是在执行“复合操作”时。以下哪个场景属于文档所指的“复合操作”？",
    "options": [
      "使用 `incrementAndGet()` 方法对一个 `AtomicInteger` 进行自增。",
      "使用 `get()` 方法读取 `AtomicBoolean` 的当前值。",
      "先用 `get()` 检查 `AtomicInteger` 的值是否大于10，如果满足条件，再用 `decrementAndGet()` 对其减10。",
      "使用 `set()` 方法为一个 `AtomicLong` 设置一个新值。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "“检查后再执行”是一个典型的复合操作。在这个例子中，“检查值是否大于10”和“减10”是两个独立的操作。在检查完成和执行减法之间，其他线程可能会修改这个值，导致操作结果不符合预期。要原子性地完成这个复合操作，需要使用 `compareAndSet()` 方法在循环中尝试，直到成功为止。",
    "source": "文档中「Atomic注意事项」部分",
    "hint": "复合操作指的是由多个独立的原子操作组成，但逻辑上需要作为一个整体原子执行的步骤。"
  },
  {
    "question": "根据文档，与传统的锁机制相比，使用Atomic类实现的无锁编程风格具有什么显著优势？",
    "options": [
      "代码逻辑总是比使用锁更简单。",
      "可以完全避免线程间的竞争。",
      "能够减少线程阻塞和上下文切换的开销，提高并发性能。",
      "在任何情况下都比锁机制消耗更少的内存。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档在“Atomic 类的特性与优势”部分明确指出，Atomic类的无锁机制（基于CAS）避免了锁的竞争和线程阻塞。这意味着线程在尝试更新失败时不会被挂起，而是可以立即重试，从而减少了线程上下文切换的昂贵开销，这在高并发场景下能显著提升性能和吞吐量。",
    "source": "文档中「Atomic 类的特性与优势」部分",
    "hint": "思考传统锁在发生争用时，操作系统需要做什么来管理等待的线程？无锁机制避免了这一过程。"
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                reportEl.remove();
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            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  